Caprine beta-mannosidosis: regional differences in deficits of CNS myelin proteins

mRNA levels for central nervous system myelin proteins in myelin deficiency of caprine beta-mannosidosis

Caprine beta-mannosidosis is an inherited lysosomal storage disease that leads to a deficiency of oligodendrocytes and hypomyelination. Our previous results demonstrated that low levels of myelin-associated glycoprotein (MAG), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and proteolipid protein (PLP) found in CNS samples correlated with decreased yields of myelin. However, there was a relative preservation of myelin basic protein (MBP) in the spinal cord samples of affected goats. This report shows that the amounts of myelin protein mRNAs in the spinal cords of affected goats relative to control goats are also decreased. The levels of mRNA for MAG, MBP and PLP in affected goat spinal cords compared with those of controls were equally decreased to approximately 50% for the three myelin proteins. This suggests that the relative preservation of MBP protein in the spinal cords is not due to a higher MBP mRNA level, but might be due to a difference in post-transcriptional processes.

Myelin-associated glycoprotein (MAG) in myelin deficiency of caprine beta-mannosidosis

Caprine beta-mannosidosis is an inherited lysosomal storage disorder due to a deficiency of beta-mannosidase which cleaves beta-linked mannose residues from the ends of N-asparagine linked oligosaccharides of glycoproteins. Histological and chemical examination has revealed a deficiency of compact myelin in the brains and spinal cords of affected goats. Since myelin-associated glycoprotein (MAG) is glycosylated and its metabolism could be directly affected in this disease, we investigated the possibility of a differential treatment of MAG in caprine beta-mannosidosis in comparison to non-glycosylated myelin proteins. MAG, myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), proteolipid protein (PLP) and glial fibrillary acidic protein (GFAP) were quantified by western blot analysis in whole homogenates of spinal cords and hemispheres from affected goats at 1, 3 and 6 days of age and from normal controls. The yields of isolated myelin from the spinal cords of affected goats varied from 37 to 63% of normal and were 7% or less of normal from the hemispheres. In mutant spinal cords, the deficits of MAG, CNP and PLP measured in whole homogenates corresponded reasonably well with the decreased myelin yields, but the levels of MBP were consistently much closer to control levels than those of the other myelin proteins. A greater deficiency of PLP than MBP was also apparent in the myelin fractions purified from the affected spinal cords. In homogenates of mutant hemispheres, MAG, MBP, PLP and CNP were undetectable or at trace levels in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)